PCV and EVAP Emission Control Systems Chapter 43 Lesson 2

Positive Crankcase Ventilation (PCV) Uses engine vacuum to draw blowby gases from the crankcase into the intake manifold for burning Blowby is caused by leakage past the piston rings Reduces HC, CO, and particulates

PCV System

PCV Valve Controls flow through the system Located in the valve cover, intake manifold, or the side of the engine block Varies flow for idle, cruise, acceleration, wide open throttle, and engine-off conditions

Air-Oil Separator May be used instead of a PCV valve Makes oil vapors condense and flow back into the oil pan

Evaporative Emissions Control Systems (EVAP) Prevent fuel vapors from entering the atmosphere Before emission controls were used, vehicles vented vapors from their fuel tanks and carburetor bowls to the atmosphere

Evaporative System

Components Non-vented fuel cap Air dome or liquid-vapor separator Rollover valve Charcoal canister Purge valve

Non-Vented Fuel Cap Prevents fuel vapors from entering the atmosphere The pressure and vacuum relief valve will vent if tank pressure or vacuum levels get excessively high

Air Dome A hump formed in the top of the fuel tank Allows for fuel expansion without spillage Provides about 10% air space to allow for fuel heating and expansion

Rollover Valve Keeps liquid fuel from entering the vent line if the vehicle rolls over A metal ball or plunger valve blocks the vent line when the valve is turned over

Stores fuel vapors when the engine is not running Charcoal Canister Stores fuel vapors when the engine is not running

Purge Valve Controls the flow of vapors Operated electrically or by vacuum Located on top of the canister or in the purge line Generally allows flow when the engine is operating above idle and at operating temperature

Engine off Operation Fuel tank vapors are routed to the charcoal canister for storage Activated charcoal absorbs and holds the vapors

Engine Running Operation Above idle, ported manifold vacuum causes the purge valve to open Gases flow through the purge line Fresh air is drawn into the canister Incoming air carries gases to the intake manifold for burning

This system uses a vacuum- controlled purge valve Evaporative System This system uses a vacuum- controlled purge valve

This system uses an electronically-controlled purge solenoid Evaporative System This system uses an electronically-controlled purge solenoid

Enhanced System Provides better control Monitors the condition of the fuel system

Enhanced System

Components Fuel tank pressure sensor Canister vent solenoid Control module Service port

Fuel Tank Pressure Sensor Monitors fuel tank pressure Sends a pressure signal to the control module

Canister Vent Solenoid Electrically operated vacuum valve replaces the fresh air vent used on older canisters Closed by the control module to perform diagnostic tests on the evaporative system

Service Port Used on many enhanced evaporative emission control systems Fitting allows the connection of service tools for testing and cleaning

Enhanced System Operation Uses a normally closed, pulse-width modulated purge solenoid When energized, the purge solenoid allows vapors to flow to the intake manifold The canister vent solenoid is normally open, allowing fresh air into the canister, and may be closed by the control module during diagnostics